/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
// @ts-check
'use strict';

/**
 * Use polling to track focus of main webview and iframes within the webview
 *
 * @param {Object} handlers
 * @param {() => void} handlers.onFocus
 * @param {() => void} handlers.onBlur
 */
const trackFocus = ({ onFocus, onBlur }) => {
	const interval = 50;
	let isFocused = document.hasFocus();
	setInterval(() => {
		const isCurrentlyFocused = document.hasFocus();
		if (isCurrentlyFocused === isFocused) {
			return;
		}
		isFocused = isCurrentlyFocused;
		if (isCurrentlyFocused) {
			onFocus();
		} else {
			onBlur();
		}
	}, interval);
};

const getActiveFrame = () => {
	return /** @type {HTMLIFrameElement} */ (document.getElementById('active-frame'));
};

const getPendingFrame = () => {
	return /** @type {HTMLIFrameElement} */ (document.getElementById('pending-frame'));
};

const defaultCssRules = `
	body {
		background-color: var(--vscode-editor-background);
		color: var(--vscode-editor-foreground);
		font-family: var(--vscode-font-family);
		font-weight: var(--vscode-font-weight);
		font-size: var(--vscode-font-size);
		margin: 0;
		padding: 0 20px;
	}

	img {
		max-width: 100%;
		max-height: 100%;
	}

	a {
		color: var(--vscode-textLink-foreground);
	}

	a:hover {
		color: var(--vscode-textLink-activeForeground);
	}

	a:focus,
	input:focus,
	select:focus,
	textarea:focus {
		outline: 1px solid -webkit-focus-ring-color;
		outline-offset: -1px;
	}

	code {
		color: var(--vscode-textPreformat-foreground);
	}

	blockquote {
		background: var(--vscode-textBlockQuote-background);
		border-color: var(--vscode-textBlockQuote-border);
	}

	::-webkit-scrollbar {
		width: 10px;
		height: 10px;
	}

	::-webkit-scrollbar-thumb {
		background-color: var(--vscode-scrollbarSlider-background);
	}
	::-webkit-scrollbar-thumb:hover {
		background-color: var(--vscode-scrollbarSlider-hoverBackground);
	}
	::-webkit-scrollbar-thumb:active {
		background-color: var(--vscode-scrollbarSlider-activeBackground);
	}`;

/**
 * @typedef {{ postMessage: (channel: string, data?: any) => void, onMessage: (channel: string, handler: any) => void }} HostCommunications
 */

/**
 * @param {HostCommunications} host
 */
module.exports = function createWebviewManager(host) {
	// state
	let firstLoad = true;
	let loadTimeout;
	let pendingMessages = [];
	let isInDevelopmentMode = false;

	const initData = {
		initialScrollProgress: undefined
	};

	/**
	 * @param {HTMLDocument?} document
	 * @param {HTMLElement?} body
	 */
	const applyStyles = (document, body) => {
		if (!document) {
			return;
		}

		if (body) {
			body.classList.remove('vscode-light', 'vscode-dark', 'vscode-high-contrast');
			body.classList.add(initData.activeTheme);
		}

		if (initData.styles) {
			for (const variable of Object.keys(initData.styles)) {
				document.documentElement.style.setProperty(`--${variable}`, initData.styles[variable]);
			}
		}
	};

	/**
	 * @param {MouseEvent} event
	 */
	const handleInnerClick = (event) => {
		if (!event || !event.view || !event.view.document) {
			return;
		}

		let baseElement = event.view.document.getElementsByTagName('base')[0];
		/** @type {any} */
		let node = event.target;
		while (node) {
			if (node.tagName && node.tagName.toLowerCase() === 'a' && node.href) {
				if (node.getAttribute('href') === '#') {
					event.view.scrollTo(0, 0);
				} else if (node.hash && (node.getAttribute('href') === node.hash || (baseElement && node.href.indexOf(baseElement.href) >= 0))) {
					let scrollTarget = event.view.document.getElementById(node.hash.substr(1, node.hash.length - 1));
					if (scrollTarget) {
						scrollTarget.scrollIntoView();
					}
				} else {
					host.postMessage('did-click-link', node.href);
				}
				event.preventDefault();
				break;
			}
			node = node.parentNode;
		}
	};

	/**
	 * @param {KeyboardEvent} e
	 */
	const handleInnerKeydown = (e) => {
		host.postMessage('did-keydown', {
			key: e.key,
			keyCode: e.keyCode,
			code: e.code,
			shiftKey: e.shiftKey,
			altKey: e.altKey,
			ctrlKey: e.ctrlKey,
			metaKey: e.metaKey,
			repeat: e.repeat
		});
	};

	const onMessage = (message) => {
		host.postMessage(message.data.command, message.data.data);
	};

	let isHandlingScroll = false;
	const handleInnerScroll = (event) => {
		if (!event.target || !event.target.body) {
			return;
		}
		if (isHandlingScroll) {
			return;
		}

		const progress = event.currentTarget.scrollY / event.target.body.clientHeight;
		if (isNaN(progress)) {
			return;
		}

		isHandlingScroll = true;
		window.requestAnimationFrame(() => {
			try {
				host.postMessage('did-scroll', progress);
			} catch (e) {
				// noop
			}
			isHandlingScroll = false;
		});
	};

	document.addEventListener('DOMContentLoaded', () => {
		if (!document.body) {
			return;
		}

		host.onMessage('styles', (_event, variables, activeTheme) => {
			initData.styles = variables;
			initData.activeTheme = activeTheme;

			const target = getActiveFrame();
			if (!target) {
				return;
			}

			if (target.contentDocument) {
				applyStyles(target.contentDocument, target.contentDocument.body);
			}
		});

		// propagate focus
		host.onMessage('focus', () => {
			const target = getActiveFrame();
			if (target) {
				target.contentWindow.focus();
			}
		});

		// update iframe-contents
		host.onMessage('content', (_event, data) => {
			const options = data.options;

			const text = data.contents;
			const newDocument = new DOMParser().parseFromString(text, 'text/html');

			newDocument.querySelectorAll('a').forEach(a => {
				if (!a.title) {
					a.title = a.getAttribute('href');
				}
			});

			// apply default script
			if (options.allowScripts) {
				const defaultScript = newDocument.createElement('script');
				defaultScript.textContent = `
					const acquireVsCodeApi = (function() {
						const originalPostMessage = window.parent.postMessage.bind(window.parent);
						let acquired = false;

						let state = ${data.state ? `JSON.parse(${JSON.stringify(data.state)})` : undefined};

						return () => {
							if (acquired) {
								throw new Error('An instance of the VS Code API has already been acquired');
							}
							acquired = true;
							return Object.freeze({
								postMessage: function(msg) {
									return originalPostMessage({ command: 'onmessage', data: msg }, '*');
								},
								setState: function(newState) {
									state = newState;
									originalPostMessage({ command: 'do-update-state', data: JSON.stringify(newState) }, '*');
									return newState;
								},
								getState: function() {
									return state;
								}
							});
						};
					})();
					delete window.parent;
					delete window.top;
					delete window.frameElement;
				`;

				newDocument.head.prepend(defaultScript);
			}

			// apply default styles
			const defaultStyles = newDocument.createElement('style');
			defaultStyles.id = '_defaultStyles';
			defaultStyles.innerHTML = defaultCssRules;
			newDocument.head.prepend(defaultStyles);

			applyStyles(newDocument, newDocument.body);

			const frame = getActiveFrame();
			const wasFirstLoad = firstLoad;
			// keep current scrollY around and use later
			let setInitialScrollPosition;
			if (firstLoad) {
				firstLoad = false;
				setInitialScrollPosition = (body, window) => {
					if (!isNaN(initData.initialScrollProgress)) {
						if (window.scrollY === 0) {
							window.scroll(0, body.clientHeight * initData.initialScrollProgress);
						}
					}
				};
			} else {
				const scrollY = frame && frame.contentDocument && frame.contentDocument.body ? frame.contentWindow.scrollY : 0;
				setInitialScrollPosition = (body, window) => {
					if (window.scrollY === 0) {
						window.scroll(0, scrollY);
					}
				};
			}

			// Clean up old pending frames and set current one as new one
			const previousPendingFrame = getPendingFrame();
			if (previousPendingFrame) {
				previousPendingFrame.setAttribute('id', '');
				document.body.removeChild(previousPendingFrame);
			}
			if (!wasFirstLoad) {
				pendingMessages = [];
			}

			const newFrame = document.createElement('iframe');
			newFrame.setAttribute('id', 'pending-frame');
			newFrame.setAttribute('frameborder', '0');
			newFrame.setAttribute('sandbox', options.allowScripts ? 'allow-scripts allow-forms allow-same-origin' : 'allow-same-origin');
			newFrame.style.cssText = 'display: block; margin: 0; overflow: hidden; position: absolute; width: 100%; height: 100%; visibility: hidden';
			document.body.appendChild(newFrame);

			// write new content onto iframe
			newFrame.contentDocument.open('text/html', 'replace');

			newFrame.contentWindow.addEventListener('keydown', handleInnerKeydown);

			newFrame.contentWindow.addEventListener('DOMContentLoaded', e => {
				const contentDocument = e.target ? (/** @type {HTMLDocument} */ (e.target)) : undefined;
				if (contentDocument) {
					applyStyles(contentDocument, contentDocument.body);
				}
			});

			newFrame.contentWindow.onbeforeunload = () => {
				if (isInDevelopmentMode) { // Allow reloads while developing a webview
					host.postMessage('do-reload');
					return false;
				}

				// Block navigation when not in development mode
				console.log('prevented webview navigation');
				return false;
			};

			const onLoad = (contentDocument, contentWindow) => {
				if (contentDocument && contentDocument.body) {
					// Workaround for https://github.com/Microsoft/vscode/issues/12865
					// check new scrollY and reset if neccessary
					setInitialScrollPosition(contentDocument.body, contentWindow);
				}

				const newFrame = getPendingFrame();
				if (newFrame && newFrame.contentDocument && newFrame.contentDocument === contentDocument) {
					const oldActiveFrame = getActiveFrame();
					if (oldActiveFrame) {
						document.body.removeChild(oldActiveFrame);
					}
					// Styles may have changed since we created the element. Make sure we re-style
					applyStyles(newFrame.contentDocument, newFrame.contentDocument.body);
					newFrame.setAttribute('id', 'active-frame');
					newFrame.style.visibility = 'visible';
					newFrame.contentWindow.focus();

					contentWindow.addEventListener('scroll', handleInnerScroll);

					pendingMessages.forEach((data) => {
						contentWindow.postMessage(data, '*');
					});
					pendingMessages = [];
				}
			};

			clearTimeout(loadTimeout);
			loadTimeout = undefined;
			loadTimeout = setTimeout(() => {
				clearTimeout(loadTimeout);
				loadTimeout = undefined;
				onLoad(newFrame.contentDocument, newFrame.contentWindow);
			}, 200);

			newFrame.contentWindow.addEventListener('load', function (e) {
				if (loadTimeout) {
					clearTimeout(loadTimeout);
					loadTimeout = undefined;
					onLoad(e.target, this);
				}
			});

			// Bubble out link clicks
			newFrame.contentWindow.addEventListener('click', handleInnerClick);

			// set DOCTYPE for newDocument explicitly as DOMParser.parseFromString strips it off
			// and DOCTYPE is needed in the iframe to ensure that the user agent stylesheet is correctly overridden
			newFrame.contentDocument.write('<!DOCTYPE html>');
			newFrame.contentDocument.write(newDocument.documentElement.innerHTML);
			newFrame.contentDocument.close();

			host.postMessage('did-set-content', undefined);
		});

		// Forward message to the embedded iframe
		host.onMessage('message', (_event, data) => {
			const pending = getPendingFrame();
			if (!pending) {
				const target = getActiveFrame();
				if (target) {
					target.contentWindow.postMessage(data, '*');
					return;
				}
			}
			pendingMessages.push(data);
		});

		host.onMessage('initial-scroll-position', (_event, progress) => {
			initData.initialScrollProgress = progress;
		});

		host.onMessage('devtools-opened', () => {
			isInDevelopmentMode = true;
		});

		trackFocus({
			onFocus: () => host.postMessage('did-focus'),
			onBlur: () => host.postMessage('did-blur')
		});

		// Forward messages from the embedded iframe
		window.onmessage = onMessage;

		// signal ready
		host.postMessage('webview-ready', process.pid);
	});
};
